Is there an alternator belt adjuster on a 1994 Geo Prism 1.8?

If the alternator is driven by a drive belt, the answer is yes. You adjust the tension by loosing the bolts on the alternator mounting brackets and sliding the alternator until the proper tension, (around 1/4" deflection at mid point of the belt) is achieved. If however it has a Serpentine Belt driving the alternator, then there is no adjustment. Tension is held by the idler pulley. If it is loose then the belt is worn out, the idler tensioner is defective, or both.